An investigation into antisemitism inside the Labour Party is “an appalling indictment of the Labour leadership”, according to the Jewish former Labour minister Dame Margaret Hodge.
The Equality and Human Rights Commission has launched a formal probe into the party after it received a “number of complaints”.
The Commission said it’s investigating whether Labour "unlawfully discriminated against, harassed or victimised people because they are Jewish".
Dame Margaret has called it a “truly disgraceful day” for Labour, and laid the blame at the feet of Labour leader Jeremy Corbyn.
Writing on Twitter, the Jewish MP said: "One of the most depressing in my 56 years as a member. Corbyn has completely failed from day one to take this issue seriously.
"The consequence is a full statutory investigation, he should hang his head in shame."
Labour has said it will “cooperate fully” with the Commission, and rejects "any suggestion that the party does not handle antisemitism complaints fairly and robustly".
“There has been a deeply worrying rise in antisemitism in the UK and across Europe,” a Labour spokeswoman said.
“We are taking action to root it out of our party by strengthening our rules and procedures”.
Labour MP Neil Coyle has been one of the first sitting MPs to react to the investigation.
The Bermondsey and Old Southwark MP said the party was able to act swiftly in expelling Alastair Campbell for voting for the Liberal Democrats, but failed “to tackle long-standing allegations of antisemitism, abuse and bullying.”
The Equality and Human Rights Commission is likely to request interviews with key players in the party, and can demand access to emails and other correspondence.
It will not be able to fine or prosecute anyone; however it can create a legally-enforceable action plan for the party.
Separately, the Muslim Council of Britain has urged the EHRC to also investigate the Conservative Party over allegations of Islamophobia.
It said there is a “tolerance for Islamophobia at the highest levels” of the party.
A spokeswoman for the EHRC said: “We have received complaints regarding the Conservative Party and are considering them in line with our usual processes.”